Light source with optimized flash energy input to gas tube

ABSTRACT

Input control circuitry for a gas discharge lamp is coupled in voltage sensing relation with a discharge capacitor and in controlling relation with a gate controlled, bilaterally conductive device connected between the capacitor and the lamp, thereby to control the conduction timing of the device in relation to occurrence of capacitor peak or near peak voltage for optimizing flash energy input from the capacitor to the lamp via the device.

United States Patent 1191 Helmuth 14 1 Mar. 11, 1975 1 LIGHT SOURCE WITH OPTIMIZED FLASH ENERGY INPUT TO GAS TUBE [75] Inventor: James G. Helmuth, Monrovia, Calif.

[73] Assignee: Chadwick-Helmuth Electronics, Inc.,

Monrovia, Calif.

22 Filed: June 19, 1973 211 Appl. No; 371,396

[52] U.S. Cl 315/200 A, 315/227, 315/240, 315/362 [51] Int. Cl. H05b 37/00 [58] Field of Search 1. 315/200 A, 200 R, 227, 315/238, 240, 241 R, 289,290, 362

[56] References Cited UNITED STATES PATENTS 3,344,311 Nuckolls 315/200 R X 11/1967 Nuckolls 315/200 A X 8/1970 Michalski 315/238 Primary ExaminerRudolph V. Rolinec Assistant Examiner-Lawrence J. Dahl Attorney, Agent, or Firm-William W. Haefliger 57 ABSTRACT 8 Claims, 9 Drawing Figures 1 V V Y V I' D s/Lflraenu. V 17 co/vouc T/ vE DEV/CE 15 19 E SLOPE DE TEC r02 7- C HIGH r02 T1765 We GENE/Q1? T08 C ONT/e01. 80 c l LIGHT SOURCE WITH OPTIMIZED FLASH ENERGY INPUT TO GAS TUBE BACKGROUND OF THE INVENTION This invention relates generally to light flash producing circuitry, and more particularly concerns simplifications overcoming certain problems in prior flasher circuits, and also eliminating need for bulky transformer structure.

Flasher circuits broadly employ means to effect sudden discharge of a capacitor through a gas tube or lamp at predetermined intervals. An example of such a circuit is found in US Pat. No. 3,524,102 to Michalski. Certain problems in such prior flashers include discoloration at the surface of the lamp, the necessity for a large, costly step-up transformer or transformers (i.e., around 1,000 watt size) and the need for time delay means in starting circuits.

SUMMARY OF THE INVENTION It is a major object of the invention to provide a flasher circuit overcoming the above described prior difficulties and problems; and which is particularly well adapted to use as a light source in graphic'reproduction devices. Basically, the flasher circuit comprises an AC power source and a discharge capacitor electrically connected to the source via an inductor; a gas discharge lamp; a gate controlled, bilaterally conductive device electrically connected between the capacitor and lamp; high voltage pulse generator electrically connected to the output side of that device, and an electrode proximate the lamp and coupled to the generator output to be responsive to high voltage pulse generation to assist or trigger ionization of the lamp gas; and, input control circuitry coupled in voltage sensing relation with the discharge capacitor and in controlling relation with said device to control its conduction timing in relation to occurrence of capacitor peak or near peak voltage, to thereby optimize flash energy input from the capacitor to the lamp, via the device. As will be seen, the trigger electrode may comprise an ion gun, and the input control circuitry may comprise a full wave rectifier, differentiating circuit means to differentiate the rectifier output wave form, and means to effect production of a control pulse in response to decrease of the output of the differentiating circuit means to a predetermined low level, the pulse applied in controlling relation to the device.

As a result, firing of the lamp occurs at peak voltage across the discharge capacitor, whatever that may be and irrespective of whether it varies; also, the gate controlled, bilaterally conductive device stays on after the capacitor discharges to supply current to the tube, keeping it ionized. Accordingly, self-regulation is achieved, and the same amount of low-level current is always supplied to the lamp because the capacitor always discharges at peak or near peak voltage. Further, discoloration of the gas lamp is avoided and light output is not inhibited by such discoloration. In this regard, prior practice involving wrapping of wire about the lamp, and to which high voltage was applied, resulted in discoloration of the lamp envelope at high temperatures of tube operation. Simplification is also achieved, as time-delay circuitry and bulky step-up transformers are eliminated. Ozone production is also reduced because triggering lasts only as long as required, and not for some safe longer time.

These and other objects and advantages of the invention, as well as the details of illustrative embodiments, will be more fully understood from the following description and drawings, in which:

DRAWING DESCRIPTION FIG. 1 is a circuit diagram, partly in block form,

FIGS. 2-5 are illustrative circuit diagrams;

FIGS. 6-8 are wave forms; and

FIG. 9 shows a graphic reproduction device, in elevation.

DETAILED DESCRIPTION Referring first to FIG. 1, an AC source is indicated at 10, and includes input terminal 11 connected to inductor 12. A discharge capacitor 13 is connected between lead 14 and a common or ground lead or terminal 15. A gas discharge lamp or tube 16 is connected between points 17 and 15, and a gate controlled, bilaterally conductive devide 18 is electrically connected between the capacitor and lamp, as via lead 14 and point 17.

A high voltage pulse generator 19 is electrically connected to the output side of device 18, and an electrode 20 extends in proximity to the lamp l6 and is coupled at 21 to the generator output to be responsive to high voltage pulse generation to assist in ionizing the lamp gas. That electrode may with unusual advantage, comprise a needle or other'sharply pointed ion gun means to produce a flow of ions directed at the tube or lamp 16, as by corona effect. Discoloration of the lamp, as would be produced were a non-pointed electrode wrapped about the lamp, is thereby avoided, since, if a flat plate or other large area electrode is used, ionization may not be sufficient unless the electrode is in surface contact with and over substantial extent of the lamp.

Finally, as seen in FIG. 1, input control circuitry 22 is coupled in voltage sensing relation with the capacitor 13, and in gate controlling relation with the device 18 to control the cyclic conduction timing of that device in such relation to the occurrence of capacitor peak or near peak voltage as to optimize flash energy input from the capacitor to the lamp, via device 18. As will be seen, circuitry 22 may comprise a capacitor voltage slope detector and pulse generator.

In operation, AC. power is applied at terminal 11 (see waveform A and input current waveform I, in FIG. 6). The L and C elements 12 and 13 are tuned to approximately twice power frequency, so that point B reaches a voltage much higher than A. The voltage D follows that at B (but is lower due to divider R and R and provides power but not command to the high voltage pulse generator 19. The detector 22 senses the peak voltage at B (zero slope) and delivers a pulse at C at that time. A control 24 enables adjustment (slight anticipation or delay) of the pulse time by sensing for slight rising or decreasing slope. The pulse at C fires the device 18, which conducts for either polarity at B. Sudden voltage increase to full value at D causes firing of generator 19, which produces a trigger pulse at E, effecting sudden ionization of the light flash producing tube or lamp l6. Capacitor 13 then discharges via device 18 through the tube, producing an intense flash of light. Inductor L limits the current following the flash until the input A reverses polarity. At this time, device 18 becomes non-conductive, and the cycle repeats.

When the flash tube becomes warm, it may remain ionized after voltage reversal and until the next flash I time; under these conditions, the voltage at D will be small and equal to the conducting drop across the tube. The generator 19 will then be only slightly powered, and at pulse command time will produce very little trigger voltage at E. Thus, ozone produced during the time interval of trigger voltage application is held to a minimum. If at any time the tube fails to remain ionized, full trigger voltage at E will be applied at the next command time.

In practice the control 24 may be set to produce a trigger at C slightly before the peak voltage at B is reached, (which increases the current frllowing the flash), or slightly after the peak (which minimizes the current following the flash). When the trigger at C is set before the peak, changes in AC power at A will cause an offsetting change in this current tending to keep the total power to the tube constant and the tube well ionized, with minimum of current following the flash (which produces mostly heat and little light); however, the control at 24 is ideally set to effect the trigger at C close to the peak voltage at B, so as to produce maximum flash energy and light for the available power input at A. In respect to the above, reference should be made to the corresponding waveforms A, B, C, D and E in FIG. 5, for both cold and hot conditions of the tube 16.

FIG. shows one unusually advantageous circuit that may be employed at 22 in FIG. 1. As there shown, the full wave input B is full wave rectified by the diode bridge 31 to produce'an output at F which is the same as waveform B except that the negative half-cycle is converted to positive. The signal at F is differentiated by small capacitor C to produce output waveform indicated at G. When the voltage at F is increasing, the voltage at G is positive, and holds the transistor Q1 turned on, which prevents C from discharging. When the rate of increase becomes sufficiently small, as determined by the setting of potentiometer 32, Q1 turns off and C charges. When the voltage at H reaches the firing voltage of trigger diode Q C discharges via Q through the primary of transformer 32 producing the command pulse at C (see waveform C in FIG. 6). The main capacitor 13 discharges and the voltage B becomes a low voltage. Zener diode Q3 blocks C from recharging to prevent further trigger during the half cycle.

FIG. 2 shows one form of the device 18 to comprise a bidirectional thyristor 18a. The latter conducts in either direction when gate signal C is applied as shown, and will become non-conductive when the direction of the current attempts to reverse. The conducting state corresponds to very low resistance, whereas the nonconducting state corresponds to very high resistance. The double SCR circuit seen in FIG. 3, as another modified form 18b operates in similar manner, with one SCR handling one flow direction, and the other SCR handling the other flow direction.

FIG. 4 illustrates one unusually advantageous form of pulse generator 19. The voltage at D charges the capacitor C via resistance R and the sudden increase in voltage D at command time firest triac 0, via small capacitor C C discharges via Q4 through the primary of at D reverses, and then becomes non-conducting. The cycle then repeats. If the flash tube is warm, the voltage at D is very small until command time, so C, does not charge appreciably, and very little trigger is produced. See the waveform at D in FIG. 7.

Representative commercial components are listed as follows:

Commercial Identification Q1 NPN transistor 2N3904 Q Bilateral diode 1N5760 Q Zener diode 1N5267 Q, Triac 2N6153 Lamp 16 PXA (pulsed Xenon Arc) General Electric Type PXA-45 18a Triac 2N6162 In FIG. 9, the tube or lamp 16 is located in the head 60 of a graphic reproduction device 61. Intense light from the tube is projected downwardly at 62 onto a plate 62 at which a photographic or graphic reproduction is to be made. Head 60 may enclose the FIG. 1 circuitry, and may be lightweight and portable, since no heavy transformer is needed. A stand 63 supports the head and plate.

Representative values of various waveforms are as follows:

A 240 VAC I 7 amps r.m.s.

B 600 volts (peak) D 600 volts (peak) D l5 KV (peak) cold; 1 KV (peak) hot E 400 V (peak) cold; V (peak) hot I claim 1. Flasher circuitry, comprising a. an AC. source and a discharge capacitor electrically connected to the source, via a series inductor,

b. a gas discharge lamp,

c. a gate controlled, bilaterally conductive device electrically connected between the capacitor and lamp,

d. a high voltage pulse generator electrically connected to the output side of said device, and an electrode proximate the lamp and coupled to the generator output to be responsive to high voltage pulse generation to assist in ionizing the lamp gas, and

e. input control circuitry coupled in voltage sensing relation with the discharge capacitor and in controlling relation with said device to control the conduction timing thereof in relation to occurrence of capacitor peak or near peak voltage to thereby optimize flash energy input from the capacitor to the lamp via said device, said input control circuitry comprising signal processing means including differentiating circuit means coupled to said capacitor to differentiate a signal derived from the capacitor, and means coupled to said processing means to effect production of a pulse in response to decrease of the ouput of the differentiating circuit means to a predetermined low value, said pulse applied in said controlling relation to said device.

2. Flasher circuitry, comprising a. an AC. source and a discharge capacitor electrically connected to the source, via a series inductor,

b. a gas discharge lamp,

c. a gate controlled, bilaterally conductive device electrically connectedbetween the capacitor and lamp,

d. a high voltage pulse generator electrically connected to the output side of said device, and an electrode proximate the lamp and coupled to the generator output to be responsive to high voltage pulse generation to assist in ionizing the lamp gas, and

e. input control circuitry coupled in voltage sensing relation with the discharge capacitor and in controlling relation with said device to control the conduction timing thereof in relation to occurrence of capacitor peak or near peak voltage to thereby optimize flash energy input from the capacitor to the lamp via said device, said input control circuitry including a full wave rectifier having an output terminal, differentiating circuit means coupled to said terminal to differentiate the rectifier output waveform, and means coupled to said differentiating circuit means to effect production of a pulse in response to decrease of the output of the differentiating circuit means to a predetermined low value, said pulse applied in said controlling relation to said device.

3. The flasher circuitry of claim 1 wherein said device comprises a bidirectional thyristor.

4. The flasher circuitry of claim 1 wherein said device comprises dual SCR circuit, one SCR connected to control conduction in one direction and the other SCR connected to control conduction in the opposite direc- Hon.

5. The flash circuitry of claim 1 wherein said generator comprises a transformer having a primary and a secondary, the primary coupled to the output side of said device through a discharge capacitor and gate controlled means controlling discharge of the capacitor, said means having a gate also connected with the output side'of said device, and said secondary connected with said electrode.

6. The flasher circuitry of claim 1 wherein said electrode includes a needle directed at said tube.

7. The flasher circuitry of claim 1 wherein said source includes an autotransformer.

8. The flasher circuitry of claim 1 and including a graphic reproduction device having a head supporting said lamp and from which light is projected toward a graphic reproduction zone, said device also supporting the remainder of said circuitry. 

1. Flasher circuitry, comprising a. an A.C. source and a discharge capacitor electrically connected to the source, via a series inductor, b. a gas discharge lamp, c. a gate controlled, bilaterally conductive device electrically connected between the capacitor and lamp, d. a high voltage pulse generator electrically connected to the output side of said device, and an electrode proximate the lamp and coupled to the generator output to be responsive to high voltage pulse generation to assist in ionizing the lamp gas, and e. input control circuitry coupled in voltage sensing relation with the discharge capacitor and in controlling relation with said device to control the conduction timing thereof in relation to occurrence of capacitor peak or near peak voltage to thereby optimize flash energy input from the capacitor to the lamp via said device, said input control circuitry comprising signal processing means including differentiating circuit means coupled to said capacitor to differentiate a signal derived from the capacitor, and means coupled to said processing means to effect production of a pulse in response to decrease of the ouput of the differentiating circuit means to a predetermined low value, said pulse applied in said controlling relation to said device.
 1. Flasher circuitry, comprising a. an A.C. source and a discharge capacitor electrically connected to the source, via a series inductor, b. a gas discharge lamp, c. a gate controlled, bilaterally conductive device electrically connected between the capacitor and lamp, d. a high voltage pulse generator electrically connected to the output side of said device, and an electrode proximate the lamp and coupled to the generator output to be responsive to high voltage pulse generation to assist in ionizing the lamp gas, and e. input control circuitry coupled in voltage sensing relation with the discharge capacitor and in controlling relation with said device to control the conduction timing thereof in relation to occurrence of capacitor peak or near peak voltage to thereby optimize flash energy input from the capacitor to the lamp via said device, said input control circuitry comprising signal processing means including differentiating circuit means coupled to said capacitor to differentiate a signal derived from the capacitor, and means coupled to said processing means to effect production of a pulse in response to decrease of the ouput of the differentiating circuit means to a predetermined low value, said pulse applied in said controlling relation to said device.
 2. Flasher circuitry, comprising a. an A.C. source and a discharge capacitor electrically connected to the source, via a series inductor, b. a gas discharge lamp, c. a gate controlled, bilaterally conductive device electrically connected between the capacitor and lamp, d. a high voltage pulse generator electrically connected to the output side of said device, and an electrode proximate the lamp and coupled to the generator output to be responsive to high voltage pulse generation to assist in ionizing the lamp gas, and e. input control circuitry coupled in voltage sensing relation with the discharge capacitor and in controlling relation with said device to control the conduction timing thereof in relation to occurrence of capacitor peak or near peak voltage to thereby optimize flash energy input from the capacitor to the lamp via said device, said input control circuitry including a full wave rectifier having an output terminal, differentiating circuit means coupled to said terminal to differentiate the rectifier output waveform, and means coupled to said differentiating circuit means to effect production of a pulse in response to decrease of the output of the differentiating circuit means to a predetermined low value, said pulse applied in said controlling relation to said device.
 3. The flasher circuitry of claim 1 wherein said device comprises a bidirectional thyristor.
 4. The flasher circuitry of claim 1 wherein said device comprises dual SCR circuit, one SCR connected to control conduction in one direction and the other SCR connected to control conduction in the opposite direction.
 5. The flash circuitry of claim 1 wherein said generator comprises a transformer having a primary and a secondary, the primary coupled to the output side of said device through a discharge capacitor and gate controlled means controlling discharge of the capacitor, said means having a gate also connected with the output side of said device, and said secondarY connected with said electrode.
 6. The flasher circuitry of claim 1 wherein said electrode includes a needle directed at said tube.
 7. The flasher circuitry of claim 1 wherein said source includes an autotransformer. 